The present invention relates to automatic fiber processing. More particularly, the invention relates to method and apparatus for preparing fiber samples and measurement of fiber characteristics from those samples.
When processing natural fibers, especially cotton, ensuring the desired quality of the fibers remains one of the most important considerations. The market value of the fibers depends on their quality. To this end, it is necessary to conduct constant monitoring of the raw fiber product that serves as the feedstock to be processed. Such monitoring typically occurs by means of testing that is performed on samples taken at random from the raw fed product before it is introduced into the process.
The testing aims to determine quality factors such as length, length uniformity, strength, elongation, trash, color, micronaire and fineness. Different efforts have been made to automate the standardized tests that measure these quality factors. Some of these efforts are detailed in U.S. Pat. No. 5,167,150 (tension elongation and cross-sectional properties); U.S. Pat. No. 5,907,394 (fiber strength); U.S. Pat. No. 6,040,905 (fiber color grading); U.S. Pat. No. 6,098,454 (moisture content, trash content, micronaire, maturity, length distribution, strength, elongation); which patents are hereby incorporated herein by this reference. However, the preparation of the fiber samples for these tests was normally carried out by hand or in a less than fully automated manner.
Typical steps involved in obtaining the fiber characteristics from a fiber bundle, such as a cotton sample, include the gathering of a specimen sample from a larger amount of fibers, preparing the specimen for testing and then performing a number of tests upon the prepared specimen. The step of preparing of the specimen sample for testing may involve carding and brushing of the specimen fibers. The form of the test specimen may vary depending upon the fiber characteristics that are measured. The tests performed upon such specimen may measure characteristics such as length, length uniformity, strength, elongation, micronaire, fineness, color and trash. The measured characteristics may also further be used for deriving additional parameters through calculations, regressions or such other means. Such characteristics may include those that are not easily measured directly, such as proportion of short fibers, maturity, predicted yarn parameters, consolidated fiber quality indices, etc.
Among the several pieces of equipment capable of measuring fiber quality characteristics at high speed are those manufactured by Premier Polytronics, India, which is the owner of this application, and Zellweger Uster, USA. In such systems, the measurement of length is carried out on a tapered beard sub-sample, which is obtained by gripping the fibers at a random catching point. See U.S. Pat. No. 6,085,584, which is hereby incorporated herein by this reference. In such cases, the sample contains fibers arranged so that the direction of each fiber's length extension is parallel to the direction of each other fiber's length extension. However, the ends of these fibers are not aligned with each other in a straight line along either opposite edge of the specimen.
Such a specimen broadly represents the manner in which the fibers are arranged in fiber assemblies such as sliver, roving and yam. Hence, the length measurements made with such a sample are widely used for optimizing the machinery parameters, particularly the roller settings. But these methods do not give a satisfactory estimate of the short fiber content in the sample.
A second known method of measuring short fiber characteristics is by scanning individual fibers, such as is done in Zellweger Uster's AFIS. See U.S. Pat. No. 5,270,787, which is hereby incorporated herein by this refrence. However, such a method uses a fixed upper length limit for defining the short fibers. This is likely to lead to incorrect interpretation of the results with certain varieties of cotton. Additional disadvantages inherent in this method and apparatus include the non-linear motion of the fiber across the sensor, the inability to obtain data from fibers that are not suitably arranged for measurement, and the overestimation of the fiber length that occurs upon the overlapping of more than one fiber.
A reliable estimate of the short fiber content can be obtained only if the tests are performed on a sample that has one end of each of the fibers aligned with the ends of the other fibers. With such an end-aligned sample (FIG. 2B for example), the length of the fiber extending from the aligned end represents the full length of the fibers, and so the shorter fibers can be distinguished easily from the longer fibers. This method is used in the conventional manual methods of length measurement such as the Shirley Comb Sorter or the BaerSorter array method.
Detailed explanation of the manual testing procedure with a Shirley CombSorter or the BaerSorter array is given in the British Standards Handbook. An extract of the British Standards Handbook can be found in the Butterworths Publication “Principles of Textile Testing,” by J. E. Booth. A brief description of the procedure is given below.
In the BaerSorter method, the tester uses a bed of combs, which control the fibers and enable the sample to be fractionalized into length groups. A grip, an aluminum depressor and a blunt needle are used manually by the tester to manipulate the fibers. From a sample of about 20 grams, the test sub-sample is prepared by carefully drawing and doubling fiber tufts several times until the fibers are straightened along their lengths, which in turn are rendered parallel to each other. During this preparation process, fibers are pulled out in tufts of successively shorter lengths by means of the grip, the longest first by successively dropping the combs as required. The fibers are combed, straightened and laid down on a velvet pad with the straight edge against a marked line in decreasing order of fiber length. The outline produced by the upper ends of the fibers is similar to a cumulative frequency diagram. Provided that the fibers are evenly spaced on the velvet pad, distances along the base line are proportional to the number of fibers. The shape of the distribution provides preliminary information on the length characteristics. A more detailed analysis can be performed by transferring the shape to a tracing. With this tracing, detailed information such as short fiber percentage, effective length, etc., are obtained by various geometrical constructions.
Though manual, time-consuming and labor intensive, the BaerSorter method is still considered to be the best among the available methods for measurement of short fibers. However, while these manual methods have proved to be useful reference measures for other length measuring equipment, these manual methods themselves cannot be used for regular measurement due to the unacceptable time required for performing such measurements.